The present invention is used in the control of heavy machinery used in the fabrication of machined parts and more specifically pertains to the numerical control of such machinery through the use of microcomputers.
Control systems for machine shop machinery are available in several basic configurations. The conventional approach is to have gangs of relays used to control the machine. When an operator pushes a button, a relay is closed to supply power to the appropriate machine function. Other relays controlled by sensors, such as limit switches, would also be employed to control the machine or drive a display on the operator's control panel. Since these relay circuits are specific to the machine, each different kind of machine tool requires the design of a unique set of relay controls.
Machines under numerical control are used to simplify the duty of the operator in that a paper tape containing machine instructions is used to program the machine through an entire machining process. Thus, by implementing simple logic circuits with relays, by providing instructions through a paper tape and reader, and by relying on various internal sensors and solenoids, a machine can be controlled to complete entire sequences of operations without manual assistance. However, to customize a numerical control system to a particular machine tool or specific use, the relay controls must be redesigned.
More recently, control systems have been implemented on printed circuit boards containing logic implemented from integrated circuit devices. Power amplifiers are provided to drive motors and solenoids in the machine, and operator panel lights. This is a significant improvement since integrated circuits are more reliable and less costly than relay logic.
Regardless of the technology used to implement the machine tool system, there usually are specific characteristics of the machine tool, or the use to which it will be put, which necessitate a certain amount of modification. If the control system is implemented in hardware the result will be a redesign for each installation.
A computer may also be used to implement the logic functions required to control the machine tool. Here, inputs to the computer, such as switch closures on either the operator panel or the machine tool, are digitized and sensed by the computer. Likewise, outputs are generated to drive operator panel displays and machine functions such as interlocks, coolant flow, tool indexes, remote functions, alarms and other system dependent functions. In this case the computer numerical control system software is used to customize the system to the particular end use.
A problem associated with a computed used for this purpose is that the computer programs written for each machine are necessarily different, resulting in the necessity of modifying the basic program for each new use. For example, the programs for controlling turret latches would be different from programs controlling milling machines. Beyond that, however, even identical machines used under differing circumstances would require individual programs.
These computer programs are usually written by computer specialists who may not be coveniently available at the machine shop. Additionally, a computer specialist brought in to do the programming may not be expert on the particular machine tool, and the use to which it is to be put.
In consideration of the above problem it is clear that what is needed is a numerical control system, under computer control, which can be used for controlling any machine tool and which can be modified by a resident machine designer who is not necessarily skilled in computer technology.